Whereas the present invention, which is embodied in a shaft-driven, multispeed drive, has utility in any vehicle where human pedal power is converted to rotary power for moving the vehicle, such as bicycles, tricycles, human driven airplanes, paddle boats, and the like, it has particular applicability to bicycles.
The first bicycle, or more precisely, velocipede, was probably invented in France in 1880 by Baron von Drais and the invention was described at that time as: "The principle of the invention consists in the simple idea of a seat upon two wheels propelled by the two feet acting on the ground". The rider, or more correctly, the walker, straddled a board supported by two wheels and sat on a seat just high enough that his feet could touch the ground to take steps. Because of its similarity to a hobby horse, the bicycle was nicknamed the Dandy-horse.
It also appears that pedals or cranks were next attached to the front wheels of bicycles. Subsequently, the "Ordinary" bicycle came into use in 1870. It had india rubber wheels, pedals on the front wheel which was substantially larger than the rear wheel.
The first rear drive bicycle was developed in 1879 by H. J. Lawson (the Safety Bicycle). It was the first bicycle to have its rear wheel driven by a chain from a pedal-driven crank located on a separate axle beneath the seat.
At this time, most bicycles were made in Europe. In 1885, the Pope Manufacturing Company of Hartford, Conn. displayed an American made bicycle at a trade show in London. This was the first bicycle to use a shaft drive. It was patented in 1885 and employed a bevel gear shaft instead of a chain to power the rear wheel. The idea caught on quickly because the bicycle was successfully used in races of that day. Many chainless models were made during the 1890's, but cost twice as much as bicycles driven with chains. Despite the fact that chain drives are far less efficient than direct or shaft drives, their price differential virtually drove the shafts from the market.
Subsequently, popularity of the bicycles, which at one time were important modes of transportation waned because of the development of the automobile for mass transportation. In the 1970's, bicycle popularity again rose because of interest in fitness, antipollution and the development of the variable speed bicycle also known as the "10-speed".
The concept of using a shaft drive instead of a chain drive has some inherent advantages that make it very desirable. One advantage stems from the fact that the greasy chain is eliminated. Since the chain is eliminated, so is the problem of brushing against it and getting grease on the rider's clothing or getting the rider's clothing caught in the chain. Also eliminated is the problem of the chain jumping off the sprockets as with present day derailers.
The most significant advantage of the bicycle shaft drive is the improved efficiency of the system over a conventional chain drive. The shaft drive of the present invention is estimated to be 90-95% efficient compared to a conventional chain drive that is only 50-70% efficient. This efficiency calculation also assumes that the chain drive is properly maintained and greased, which from casual observation of the average bicycles on the street is not the case.
With regard to multispeed bicycles, the shaft drive affords the opportunity to include brakes that are applied by backpedaling (coaster brakes) similar to brakes used on single speed children's bikes. Coaster brakes are possible because the shaft drive can transmit force when pedaling forwards or backwards. A shaft drive also allows direct drive similar to what single speed track bikes use. This direct drive feature is particularly advantageous for mountain bikes that are used for riding on trails because direct drives allow the rider better control of the bike. A multispeed shaft drive could, therefore, be mounted on a coaster brake hub, a direct drive hub, a ratchet hub, or a hub that combines more than one of these options. The aesthetic appeal of the shaft drive is also an advantage due to the uncluttered "high tech" and aerodynamic appearance.
On Feb. 4, 1975, U.S. Pat. No. 3,863,503 was issued to David C. Loeb et al. It disclosed a shaft-driven bicycle that was multispeed and shiftable throughout a series of gear ranges. It employed a series of ring gears rotated by the pedals and a second series of ring gears secured to the rear axle. A telescoping drive shaft had pinions on each end which were engageable with each of the sets of ring gears.
The patent acknowledged that because of the radial expansion of the gear rows in each set of concentric ring gears, an unavoidable deviation resulted in the spaces between the teeth (actually rectangular projections) of the innermost rows of teeth. It was suggested that the radial length of the teeth could be reduced. The teeth could be shaped so that the circumferential space between the teeth remained constant. However, if the spaces remain constant, the teeth of each ring gear would vary in size from ring to ring and could not engage the pinion, which had teeth of constant size and spacing. Conversely, if the teeth remained the same size, the spaces between them in the outermost ring would be greater than the spaces between them in the innermost ring and the pinion would, obviously, not engage in the spaces but would skip.
It is to the problems encountered by this construction that the present invention is directed.